In manufacturing processes for products such as semiconductor devices, thin display screens, magnetic disks and the like, substrates such as semiconductor wafers, glass substrates, disk substrates and the like are processed and the processed substrates are inspected. While being rotated, the substrate is processed and inspected in many cases. In surface inspection to determine whether or not a defect such as a flaw or the like or foreign matter exists on the front surface of a semiconductor wafer, while the semiconductor wafer is rotated, an area to be irradiated with inspection light is shifted in the radial direction of the semiconductor wafer. In this way, the inspection light spirally scans the front surface of the semiconductor wafer to detect a defect or foreign matter on the entire surface of the semiconductor wafer in a short time.
Along with miniaturization of a circuit pattern, a defect or foreign matter occurring even on the rear surface of a substrate tends to be controlled and reduced for products such as semiconductor devices, thin display screens, magnetic disks and the like. For this reason, the manufacturing process needs to process and inspect not only the front surface but the rear surface of the substrate in a non-contact state.
In view of the above, a substrate holding device is proposed that can rotate a substrate while being in non-contact with the front surface and rear surface of the substrate (for example, see Patent Documents 1 and 2).